You won't see much difference if you wall mount the R500s vertically or horizontally, due to our multiple antenna array BeamFlex technology with MU-MIMO in the 802.11ac chipset.
But you won't get the same coverage with flat wall mount, over ceiling or top of bookcase, as they were meant to be used flat/horizontal, but things depend upon your environment.
We don't make a shelf, but fabricating one, or something from a home design shop might be feasible to allow horizontal over vertical wall mounting.
Can your VAR provide a couple samples to put on a couple walls in your environment to help test your client coverage area?
https://ruckus-support.s3.amazonaws.com/private/documents/550/r500-qsg-800-70564-001-revC-20140910.p...